The field of electric dry shaving has progressed significantly in the last 40 years since such shavers were first made available commercially in the United States. During this period various basic shaving principles have been developed and perfected to a high degree from the standpoint of quality and uniformity of the product. It is well recognized by those skilled in the art that the satisfactory performance of an electric shaver depends to a large extent on whether or not it can be manufactured to the required close tolerances in order that a close and comfortable shave may be obtained. As the quality of shavers has improved, however, it has been noted that there are some inherent limitations in many of the basic shaving approaches. The recognition of these limitations has caused shaver manufacturers to modify their designs so as to utilize more than one general shaving approach in the design of their shaving heads. Explaining this situation in more specific terms, we note that it is possible to obtain the closest and most comfortable shave by utilizing a shaver having a thin, perforated, fixed shearing member or comb which is used in combination with either a reciprocating or oscillating cutter system. Because the thickness of the comb and the size of the perforations may be controlled very accurately, it is possible with this type of system to produce a shaving head which will give a very close shave with a minimum amount of skin irritation.
The perforated comb is generally less satisfactory, however, in cutting long hairs or trimming along the hair line or around the moustache since it is difficult to position a long hair properly for entrance into one of the perforations. To solve this problem various approaches such as placing slots in the comb or adding auxiliary trimmers have been attempted. While the comb slots are reasonably effective on long facial hairs, they complicate the manufacturing of the perforated comb and are relatively ineffective in trimming sideburns, moustaches and the like. The auxiliary trimmer which is normally positioned at the side or at one end of the shaving heads is satisfactory for trimming sideburns and moustaches but is inconvenient and relatively unsatisfactory as far as cutting long facial hairs during the shaving process concerned. In other words, if you miss a facial hair with the shaving head, it is necessary to move the trimmer into position to cut that specific hair. As a consequence the shavers utilizing the combination shaving head with an auxiliary trimmer have been found to be relatively unsatisfactory from the standpoint of picking up long hairs during the shaving operation.
The ultimate goal of dry shaver designers, manufacturers and users is the "one pass" electric shaver which would shave satisfactorily with one traverse across the skin in much the same way as a conventional blade type shaver will perform. To accomplish this "single pass" shaving, it is necessary to include both the shaving head and the long hair trimmer positioned so that both operate during the single pass across the face.
There have been a number of examples of multi-headed shavers which include heads adapted for shaving positioned in close proximity to heads adapted for trimming. The patent to Kleinman, U.S. Pat. No. 2,529,169 and Brauss U.S. Pat. No. 2,917,824 are noted in this regard. The patent to Berg, U.S. Pat. No. 2,574,317 shows an arrangement in which the center head of the shaver is movable for trimming purposes. The center head in U.S. Pat. No. 2,574,317 is described as having "an adjustable center head movable relative to and outwardly from [the ] side heads "and having" comparatively wide slots for cutting long hairs." None of these patents, however, provide a satisfactory solution to the problem of shaving and trimming simultaneously with a shaver and also the making available of the trimmer for use in trimming sideburns and moustaches.